When measuring a bioelectric signal, for example an electrocardiogram signal (ECG signal), via a differential voltage measuring system, interference can occur due to a common-mode interference signal. Typically, the greater the difference of a first measuring path of the differential voltage measuring system from a second measuring path of the differential voltage measuring system with respect to the impedance, the stronger the common-mode interference signal.
If the first measuring path and the second measuring path are in each case in contact with the patient's skin via electrodes, the difference with respect to the impedance can be particularly high. In many cases, the establishment of the same conditions, in particular the same impedances, at two or more electrode contact points on a patient and their maintenance throughout the duration of a measurement represents a challenge. [BC11] discloses various possibilities for the suppression of a common-mode interference signal.